Combustion Air and Exhaust Gas Arrangement of an Internal Combustion Engine

ABSTRACT

The invention relates to an arrangement for supplying an internal combustion engine ( 1 ), particularly of a motor vehicle, with a stream of combustion air ( 2 ) and for removing a stream of exhaust gas ( 3 ) from the internal combustion engine ( 1 ). The arrangement comprises a fresh air channel ( 4 ) for conveying the stream of combustion air ( 2 ), an exhaust channel ( 5 ) for conveying the stream of exhaust gas ( 3 ), an exhaust gas turbocharger ( 6 ) comprising a condenser ( 7 ) disposed in the fresh air channel ( 4 ) and comprising a turbine ( 8 ) disposed in the exhaust gas channel ( 5 ), a swirl generator ( 9 ) connected directly upstream of the condenser ( 7 ) for the stream of combustion air ( 2 ) arriving in the condenser ( 7 ), and a low-pressure exhaust gas return ( 10 ) comprising a return channel ( 11 ) emptying into the fresh air channel ( 4 ) upstream of the condenser ( 7 ) for conveying an exhaust gas return stream ( 12 ). The swirl generator ( 9 ) is designed as a centrifugal separator ( 13 ) for condensate forming in the exhaust gas return stream ( 12 ).

TECHNICAL FIELD

The invention concerns an arrangement for supplying an internal combustion engine, in particular of a motor vehicle, with a combustion air stream and for discharging an exhaust gas stream from the internal combustion engine in accordance with the features of the preamble of claim 1.

PRIOR ART

Performance, running behavior, and exhaust gas emission of internal combustion engines, in particular of motor vehicles, are affected in many respects not only by the motor itself but also by its arrangement for supply of combustion air and discharge of the exhaust gas stream. For improving performance, exhaust gas turbochargers are widely used that comprise a compressor arranged in the fresh air passage and a turbine arranged in the exhaust gas passage. At medium and high power output of the internal combustion engine such an exhaust gas turbocharger provides in the desired way a charge pressure increase of the combustion air stream and, based thereon, an increased power yield.

Under partial load, it can be advantageous to generate intake with a defined swirl at the compressor of the exhaust gas turbocharger. For this purpose, the swirl generator is arranged upstream of the compressor of the exhaust gas turbocharger and induces a swirl in the incoming combustion air stream. In this way, the operating properties of the exhaust gas turbocharger under partial load are improved.

Independent of the aforementioned problem, the prior art provides various measures in order to improve exhaust gas emissions. A known measure resides in providing a low-pressure exhaust gas return with which the exhaust gas return stream is introduced into the combustion air stream during partial load. This serves primarily for reducing pollutants, in particular for reducing the NOX emission.

Across the length of the exhaust gas return the exhaust gas return stream will cool down. This can lead to condensate formation, in particular to generation of water droplets that can damage the compressor when impinging on the compressor vanes of the exhaust gas turbocharger that rotate at high speed. For avoiding this undesirable effect condensate separators are used that at least partially remove the condensate formed in the exhaust gas stream. Constructive expenditure and cost expenditure are high. This separator is located in known configuration at a certain spacing relative to the compressor inlet so that, as the exhaust gas return stream and the combustion air stream mix with one another, an after-condensation with repeated droplet formation may begin.

It is an object of the present invention to further develop a combustion air and exhaust gas arrangement of an internal combustion engine such that the operating safety of the exhaust gas turbocharger is improved.

This object is solved by an arrangement with the features of claim 1.

SUMMARY OF THE INVENTION

An arrangement for supplying an internal combustion engine with a combustion air stream and for discharging an exhaust gas stream is proposed in which the swirl generator provided for improved partial load operation is configured as a centrifugal separator for condensate that is formed in the exhaust gas return stream.

By utilizing the centrifugal force and mass inertia forces that occur in the swirl generator and that act on the formed condensate, it is possible without any additional measures to provide an effective separation. The expenditure for an additional centrifugal separator is no longer required. With respect to the system requirements, the swirl generator is arranged for its function under partial load immediately at the compressor inlet so that a long mixing travel and thus the risk of repeated droplet formation is eliminated. Since the additional separator is not required, only a reduced mounting space is needed. The internal combustion engine including its attachment parts may be designed more compact.

It can be expedient to mix the exhaust gas return stream upstream of the swirl generator with the combustion air stream wherein the swirl generation and simultaneous condensate separation happen only once the downstream swirl generator is reached. In an advantageous further embodiment, an introduction of the exhaust gas return stream is substantially tangential in the rotational direction of the air stream in the swirl generator. In this way, the stream velocity of the exhaust gas return stream in the mixed or unmixed state is transformed directly into a swirl with simultaneously initiated separation effect. An additional energy introduction for swirl generation is not required. Expediently, in addition or as an alternative, an introduction of the exhaust gas return stream into the swirl generator is provided with an axial directional component, i.e., at an acute angle to the main flow direction of the swirl generator. The axial intake velocity of the compressor is thus improved.

In an expedient embodiment, a circumferential section of the swirl generator is provided with a radially outwardly positioned discharge groove for the separated condensate. The condensate droplets that as a result of the swirl effect are forced radially outwardly collect at the inner side of the circumferential section and enter the discharge groove under the effect of the swirl-caused centrifugal force, assisted by the carrying effect of the gas stream. The collection in the discharge groove reduces reintroduction of the separated condensate into the gas stream and allows also a controlled discharge from the centrifugal separator.

The discharge groove extends advantageously in the circumferential direction of the swirl generator about at least 180 degrees and in particular about approximately 270 degrees. In this way, it is ensured that the separated condensate can be substantially completely collected and discharged.

The cross-section of the discharge groove increases advantageously in the rotational direction of the swirl generator. In particular, a condensate discharge passage exits from the discharge groove at a terminal area of the discharge groove with respect to the rotational direction of the swirl generator. The condensate quantity that increases in the rotational direction can be reliably and completely received by the discharge groove and, by utilizing its kinetic energy that exists in the rotational direction of the swirl generator, can be discharged through the condensate discharge passage.

In an expedient further embodiment, on at least one longitudinal edge of the discharge groove a sealing lip is provided that is in particular slanted in a radial outward direction. The arrangement of the discharge groove and sealing lip acts as a trap for the separated condensate that can penetrate easily into the discharge groove but cannot leave it to return into the gas stream.

In an advantageous further embodiment the swirl generator has a central substantially straight main air passage and a swirl air passage that opens with a tangential directional component into the main air passage, wherein the return passage extends into the swirl air passage. By means of suitable control devices an auxiliary air stream that is introduced through the swirl air passage and also the exhaust gas return stream can be matched to the respective operating states of the internal combustion engine. For example, in full load operation an exhaust gas return is not used wherein the introduction of the auxiliary air stream for swirl generation can be reduced or even switched off. By means of the auxiliary air stream provided for partial load operation the exhaust gas return stream is introduced at high kinetic energy and a swirl is imparted so that, without additional measures, significant mass forces and thus an excellent separating effect will occur.

Upstream of the swirl generator there is expediently a heat exchanger arranged in the return passage that cools the exhaust gas return stream. The exhaust gas turbocharger and the internal combustion engine are supplied with cool combustion air that is enriched with returned exhaust gas so that the internal combustion engine can be operated at high power yield with reduced pollutant emissions. In connection with the increased tendency of condensate formation as a result of the cooling action of the heat exchanger, the advantages of the inventive arrangement become particularly apparent. The effective separation immediately at the inlet of the compressor ensures that a substantially condensate-free gas stream enters the compressor so that the latter has an increased operational safety.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will be explained in the following with the aid of drawing in more detail. It is shown in:

FIG. 1 as a schematic block diagram an internal combustion engine with an exhaust gas turbocharger, with a low-pressure exhaust gas return and with a swirl generator embodied as a centrifugal separator for improved partial load operation of the engine;

FIG. 2 a side view of a section of the fresh air passage with a swirl generator according to FIG. 1;

FIG. 3 an enlarged perspective illustration of the swirl generator with integrated centrifugal separator according to FIG. 2;

FIG. 4 a perspective longitudinal section illustration of the swirl generator according to FIG. 3 with details of the stream guiding action and its effect on the separation and condensate discharge in a discharge groove;

FIG. 5 a schematically enlarged cross-section illustration of the discharge groove according to FIG. 4 with sealing lips arranged at the longitudinal edges.

EMBODIMENT(S) OF THE INVENTION

FIG. 1 shows as a schematic block diagram an internal combustion engine 1 that can be a diesel engine, a gasoline engine or the like. In the illustrated embodiment the internal combustion engine 1 is provided for driving a motor vehicle. A stationary engine or the like may also be expedient. The internal combustion engine 1 is provided with an arrangement according to the invention for supplying a combustion air stream 2 and for discharging an exhaust gas stream 3. The arrangement comprises a fresh air passage 4, an exhaust gas passage 5, an exhaust gas turbocharger 6 as well as a low-pressure exhaust gas return 10 with a return passage 11.

The exhaust gas stream 3 of the internal combustion engine 1 is collected by means of an exhaust gas manifold 31 and is discharged through the exhaust gas passage 5. The combustion air stream 2 for combustion of fuel in the internal combustion engine 1 is supplied by fresh air passage 4 to the internal combustion engine 1. In this connection, it passes at the inlet side through air filter 28 arranged in the fresh air passage 4 and is supplied by means of an intake manifold 30 to the individual cylinders of the internal combustion engine 1.

The exhaust gas turbocharger 6 has a compressor 7 arranged in the fresh air passage 4 as well as a turbine 8 arranged in the exhaust gas passage 5 wherein the turbine 8 that is driven by the combustion air stream 2 guided in the exhaust gas passage 5 drives in turn the compressor 7. The compressor 7 increases the charge pressure of the combustion air stream 2 passing through the air filter 28. For reducing the temperature increase of the combustion air stream 2 that is caused thereby, a charge air cooler 29 is arranged between the compressor 7 and the intake manifold 30.

By means of the return passage 11 of the low-pressure exhaust gas return 10 at certain operating states of the internal combustion engine 1, in particular at partial load, an exhaust gas return stream 12 is branched off the exhaust gas stream 3 and is admixed to the combustion air stream 2 upstream of the exhaust gas turbocharger 6.

Under comparable operating conditions, and in particular for improving the operating behavior of the exhaust gas turbocharger at minimal engine load and low engine speed, the combustion engine 1 is operated with swirl-loaded compressor intake. For this purpose, in the fresh air passage 4 a swirl generator 9 is arranged that is arranged upstream of the compressor 7 immediately at the inlet. The swirl generator 9 impresses a swirl on the combustion air stream 2 entering the compressor 7 in a way disclosed in the following in more detail. The swirl generator 9 is moreover embodied in a way described also in more detail in the following as a centrifugal separator 13 for the condensate that is formed in the exhaust gas return stream 12. The condensate is separated in the centrifugal separator 13 and in accordance with arrow 43 is discharged from the swirl generator 9 and can be collected, treated further, or returned into the engine.

It can be expedient to connect a simple fresh air passage 4 without further branches coaxially and centrally to the compressor 7. In this connection, the incoming combustion air stream 2, for example, by means of aerodynamic vanes or the like, is impressed with a swirl so that the response behavior of the exhaust gas turbocharger 6 is improved. This swirl acts also on the exhaust gas return stream 12 that is admixed upstream so that the separating effect described in the following is generated. In the illustrated embodiment, the fresh air passage 4 between the air filter 28 and the compressor 7 has a branch 32 so that downstream of the branch 32 a main air passage 21 and a swirl air passage 22 are fluidically connected in parallel. In the main air passage 21 and in the swirl air passage 22 optionally a control device 26, 27 is arranged, respectively, by means of which a main air stream 24 in the main air passage 21 as well as an auxiliary air stream 25 in the swirl air passage 22 can be controlled or governed with regard to their quantity. The swirl air passage 22 opens into the swirl generator 9 where the auxiliary air stream 25 and the main air stream 24 are joined with one another immediately upstream of the compressor 7. By means of the auxiliary gas stream 25 a swirl is generated in a way to be described in the following in more detail that acts not only proportionally on the auxiliary air stream 25 but also on the main air stream 24 so that the exhaust gas turbocharger 6 operates with swirl enhancement. In this way, the operating properties of the exhaust gas turbocharger under partial load and at low engine speed are improved. For certain operating states it can be expedient to reduce or even shut off the swirl-generating auxiliary air stream 25 by means of the control device 27. In this state, the exhaust gas turbocharger 6 is supplied primarily with the substantially swirl-free combustion air of the main air stream 24 that in turn can be controlled or governed by means of control device 26.

The return passage 11 opens into the swirl air passage 22 downstream of the correlated control device 27 and upstream of the swirl generator 9. Upstream of the swirl generator 9 a heat exchanger 23 that cools the exhaust gas return stream 12 is arranged in the return passage 11. Depending on the position of the control device 27 more or less combustion air in the form of the auxiliary air stream 25 is admixed to the exhaust gas stream 12. The mixture of the auxiliary air stream 25 and the exhaust gas return stream 12, optionally also the exhaust gas return stream 12 alone, is imparted with a swirl in the swirl generator 9. Condensate in the exhaust gas return stream 12 which is formed in particular downstream of the heat exchanger 23 as a result of its cooling action is separated in the centrifugal separator 13, integrated in the swirl generator 9, immediately upstream of the compressor 7 and is discharged in accordance with the arrow 43. As a result of this, substantially condensate-free mixture of combustion air and returned exhaust gas is supplied to the compressor 7.

FIG. 2 shows in a side view a section of the fresh air passage 4 according to FIG. 1 in the area of the main air passage 21, the swirl air passage 22, and the swirl generator 9. The swirl generator 9 is flange-connected immediately at the intake side of the schematically indicated compressor 7 at its end face. The main air passage 21 with the main air stream 24 opens substantially straight into the compressor 7. In addition to the main air passage 21 the swirl air passage 22 is part of the fresh air passage 4 and branches off the auxiliary air stream 25 at the branch 32 from the combustion air stream 2. The schematically indicated return passage 11 opens upstream of the swirl generator 9 into the swirl air passage 22 where the exhaust gas return stream 12 is mixed with the auxiliary air stream 25. This mixture is substantially introduced tangentially with an axial directional component into the swirl generator 9 and is subjected thereby to a swirl with a rotational direction that is indicated by arrow 33. This swirl is also imparted to the central main air stream 24. By entraining the exhaust gas return stream 12 with the auxiliary air stream 25 the introduction of the exhaust gas return stream 12 is realized with the same rotational direction as the air stream in the swirl generator.

Further details of the swirl generation with integrated condensate separation result from the perspective illustration according to FIG. 3 in which the swirl generator 9 according to FIG. 2 is shown as an individual part. Same features are identified with same reference numerals. The swirl generator 9 comprises a central approximately cylindrical pipe section 34 with a longitudinal axis 38. When looking also at FIG. 2, it can be seen that the substantially straight pipe section 34 is part of the central main air passage 21 through which the main air stream 24 is guided straight and axis-parallel to the longitudinal axis 38 in accordance with arrow 37. The swirl air passage 22 opens tangentially as well as at a slant toward the longitudinal axis 38 into the swirl generator 9 wherein the swirl air passage 22 extends with an tangential and with an axial directional component into the main air passage 21. This introduction is realized by means of a spiral section 35 that extends externally about the pipe section 34 in which the gas stream of the swirl air passage 22 that enters in accordance with arrow 36 with tangential and axial directional component is subjected to a swirl effect. Within the swirl generator 9 the various gas streams are mixed in accordance with arrows 36, 37, 39 to a total gas stream with swirl and axial directional component in accordance with arrow 40.

For forming the centrifugal separator 13, the swirl generator 9 in the area of its spiral section 35 has a circumferential section 15 in the form of a circumferential wall in which, at the radial outer circumference, an inwardly open discharge groove 16 for separated condensate is formed integrally. Relative to the intake of the gas in accordance with arrow 36 the discharge groove 16 extends in the circumferential direction of the swirl generator 9 about at least 180 degrees. In the illustrated embodiment it extends in accordance with arrow 39 about approximately 270 degrees about the longitudinal axis 38. Relative to the rotational direction of the air stream in the swirl generator 9, as indicated by arrow 40, the discharge groove 16 has a terminal area 20 in the rotational direction 40. A condensate discharge passage 19 is provided that extends from this terminal area 20 away from the discharge groove 16 and, in accordance with the illustration of FIG. 1, discharges the separated condensate in accordance with the illustrated arrow 43.

FIG. 4 shows a longitudinal section illustration of the swirl generator 9 according to FIG. 3. The circumferential section 15 of the spiral section 35 provided for forming the centrifugal separator 13 surrounds a cylindrical inner wall 41 of the pipe section 34 that projects partially in the longitudinal direction wherein, in accordance with arrow 42, a fluidic connection between the spiral section 35 and the pipe section 34 exists however. Relative to the flow direction in the spiral section 35, indicated by the arrow 42, its cross-section in the axial direction of the swirl generator 9 becomes more narrow so that along the circumferential path an increasing proportion of gas stream introduced in accordance with arrow 42 is mixed into the main air stream 24 (FIG. 2) in the pipe section 34. The main air stream 24 (FIG. 2) has a main flow direction 14 in accordance with the illustration of FIG. 4. As a result of the slant of the swirl air passage 22 relative to the longitudinal axis 38 of the main air passage 21 that deviates from 90 degrees and is illustrated in FIG. 3 and the narrowing cross-sectional shape of the spiral section 35, an introduction of the exhaust gas return stream 12 together with the auxiliary air stream 25 (FIG. 2) into the swirl generator 9 is realized not only substantially tangential but also with an axial directional component parallel to the main flow direction 14 of the swirl generator 9 in accordance with arrow 42 (FIG. 3).

The illustration according to FIG. 4 shows that the cross-section of the discharge groove 16 in the rotational direction of the swirl generator 9 is enlarged in accordance with arrow 42. In the embodiment illustrated in FIG. 4 the cross-section of the discharge groove 16 increases in the width direction as well as in the depth direction.

Further details for configuring the discharge groove 16 can be seen in the schematic cross-sectional illustration of FIG. 5. The discharge groove 16 integrally formed in the circumferential section 15 is limited relative to its open side by longitudinal edges 17. At both longitudinal edges 17 schematically indicated sealing lips 18 are arranged that in the illustrated cross-sectional illustration beginning at the longitudinal edges 17 converge and, in doing so, are slanted slightly radially outwardly, i.e., in the direction of the bottom of the discharge groove 16. In this way, the condensate that has been separated can enter the discharge groove 16 but cannot return or return only with difficulty into the spiral section 35 (FIG. 4). 

1. Arrangement for supplying an internal combustion engine (1), in particular a motor vehicle, with a combustion air stream (2) and for discharging an exhaust gas stream (3) from the internal combustion engine (1), comprising a fresh air passage (4) for guiding the combustion air stream (2), an exhaust gas passage (5) for guiding the exhaust gas stream (3), an exhaust gas turbocharger (6) with a compressor (7) arranged in the fresh air passage (4) and with a turbine (8) arranged in the exhaust gas passage (5), a swirl generator (9) arranged immediately upstream of the compressor (7) for the combustion air stream entering the compressor (7), as well as a low-pressure exhaust gas return (10) with a return passage (11) opening upstream of the compressor (7) into the fresh air passage (4) for guiding an exhaust gas return stream (12), characterized in that the swirl generator (9) is embodied as a centrifugal separator (15) for condensate forming in the exhaust gas return stream (12) or for particles.
 2. Arrangement according to claim 1, characterized in that an introduction of the exhaust gas return stream (12) into the swirl generator (9) is provided substantially tangentially in the rotational direction of the swirl generator (9).
 3. Arrangement according to claim 1, characterized in that an introduction of the exhaust gas return stream (12) into the swirl generator (9) is provided with an axial directional component at an acute angle to the main flow direction (14) of the swirl generator (9).
 4. Arrangement according to claim 1, characterized in that a circumferential section (15) of the swirl generator (9) is provided with a radial outwardly positioned discharge groove (16) for separated condensate.
 5. Arrangement according to claim 4, characterized in that the discharge groove (16) in the circumferential direction of the swirl generator (9) extends about at least 180 degrees.
 6. Arrangement according to claim 4, characterized in that the cross-section of the discharge groove (16) increases in the rotational direction of the swirl generator (9).
 7. Arrangement according to claim 4, characterized in that a condensate discharge passage (19) relative to the rotational direction of the swirl generator (9) extends away from the discharge groove in a terminal area (20) of the discharge groove (16).
 8. Arrangement according to claim 4, characterized in that on at least one longitudinal edge (17) of the discharge groove (16) a particularly radial outwardly slanted sealing lip (18) is arranged.
 9. Arrangement according to claim 1, characterized in that the swirl generator (9) has a central, substantially straight extending main air passage (21) and a swirl air passage (22) that opens with a tangential directional component into the main air passage (21), wherein the return passage (11) is guided into the swirl air passage (22).
 10. Arrangement according to claim 1, characterized in that upstream of the swirl generator (9) a heat exchanger (23) that cools the exhaust gas return stream (12) is arranged in the return passage (11).
 11. Arrangement according to claim 5, wherein the discharge groove (16) in the circumferential direction of the swirl generator (9) extends approximately 270 degrees.
 12. Arrangement according to claim 2, wherein an introduction of the exhaust gas return stream (12) into the swirl generator (9) is provided with an axial directional component-at an acute angle to the main flow direction (14) of the swirl generator (9); wherein a circumferential section (15) of the swirl generator (9) is provided with a radial outwardly positioned discharge groove (16) for separated condensate; and wherein the discharge groove (16) in the circumferential direction of the swirl generator (9) extends about at least 180 degrees.
 13. Arrangement according to claim 12, wherein the discharge groove (16) in the circumferential direction of the swirl generator (9) extends approximately 270 degrees.
 14. Arrangement according to claim 12, wherein the cross-section of the discharge groove (16) increases in the rotational direction of the swirl generator (9); wherein a condensate discharge passage (19) relative to the rotational direction of the swirl generator (9) extends away from the discharge groove in a terminal area (20) of the discharge groove (16); and wherein on at least one longitudinal edge (17) of the discharge groove (16) a particularly radial outwardly slanted sealing lip (18) is arranged.
 15. Arrangement according to claim 14, wherein the swirl generator (9) has a central, substantially straight extending main air passage (21) and a swirl air passage (22) that opens with a tangential directional component into the main air passage (21); and wherein the return passage (11) is guided into the swirl air passage (22).
 16. Arrangement according to claim 15, wherein upstream of the swirl generator (9) a heat exchanger (23) that cools the exhaust gas return stream (12) is arranged in the return passage (11). 